Last night it was fascinating to see that thunderstorms formed just off shore the Dutch coast and over interior lakes and estuaries:
It is believed that they were triggered by a so called theta-hill effect: an offshore flow of warm continental air 'collides' with relatively cold air in the lowest few hundered feet and is forced to rise, just like a flow over hills or mountain ridges. In this case the shallow cold air just offshore is the boundary. Also the development of a nocturnal low level jet contributes to the forced rising motion.
The 00 UTC sounding of De Bilt shows this low level jet and also that thunderstorms couldn't start from the surface:
CAPE was more than sufficient for the development of strong storms. Radar indicated top heights were 45,000 ft and there was a report of large amounts of hail in a coastal town (caused by the storm formed over Lake IJsselmeer).
Glad that I had the nightshift during that time, it was great to watch the lightning in the far northwest.
It is believed that they were triggered by a so called theta-hill effect: an offshore flow of warm continental air 'collides' with relatively cold air in the lowest few hundered feet and is forced to rise, just like a flow over hills or mountain ridges. In this case the shallow cold air just offshore is the boundary. Also the development of a nocturnal low level jet contributes to the forced rising motion.
The 00 UTC sounding of De Bilt shows this low level jet and also that thunderstorms couldn't start from the surface:
CAPE was more than sufficient for the development of strong storms. Radar indicated top heights were 45,000 ft and there was a report of large amounts of hail in a coastal town (caused by the storm formed over Lake IJsselmeer).
Glad that I had the nightshift during that time, it was great to watch the lightning in the far northwest.
